Multi-level band-restricted waveform generator

Abstract

A multi-level band-restricted waveform generator in which a modulation wave prior to band restriction (M-level signal sequence) is broken into elementary waveforms and a plurality (N-nary) of prestored waveform components corresponding to the elementary waveforms after predetermined band restrictions are read out of a read-only memory for generating waveform components and added to generate a desired multi-level band-restricted waveform.

What we claim is: 
     
       1. A multi-level band-restricted waveform generator for deriving a multi-level band-restricted waveform from an M-level (a natural number, M-2) signal sequence, comprising: a read-only memory wherein M kinds of waveforms on N symbol periods define one symbol group, each of which takes one of M levels from said M-level signal sequence on one symbol period and takes the value zero on all the other (N-1) symbol periods in said one symbol group, are used as elementary waveforms, the band-restricted waveform of (k/N)-th symbol group (where (K/N)=(x) is the smallest integer greater than x and k is the symbol length of an impulse response determined by said band restriction) corresponding to a sequence of (k/N) elementary waveforms is precalculated as waveform components, and said waveform components are stored in a memory block identified by block addresses each composed of an M-level sequence with a length of (k/N) digits corresponding to said sequence of (k/N) elementary waveforms, in the order of time series specified by an additional scanning address;   a block address selector wherein N sets of M-level signal sequences for specifying the first to the N-th sequences each including (k/N) elementary waveforms, formed so that the sum of said elementary waveforms of each set is equal to said M-level signal sequence, are selected on a time-shared basis and provided as said block addresses to said read-only memory;   a scanning address generator wherein N scanning addresses shifted from each other by a 1/N period (one symbol period) are selected on a time-shared basis in synchronization with the time-shared selection of said block addresses and provided as said additional scanning addresses to said read only memory;   a demultiplexer wherein N parallel outputs are obtained by demultiplexing N waveform components read out of said read-only memory on a time-shared basis; and   an adder wherein said outputs are added together and output as said multi-level band-restricted waveform.   
     
     
       2. A multi-level band-restricted wave form generator for deriving a multi-level band-restricted waveform from M-level (a natural number, M-2) signal sequence, comprising: a read-only memory wherein M kinds of waveforms on N (plural) symbol periods defined as one symbol group, each of which takes specified levels on each symbol period on said one symbol group so that the sum of said specified levels of said one symbol group becomes equal to any one of M levels from said M-level signal sequence, are used as elementary waveforms, the band-restricted waveform of (k/N)-th symbol group (where (K/N)=(x) is the smallest integer greater than x and k is the symbol length of an impulse response determined by said band restriction) corresponding to a sequence of (k/N) elementary waveforms is precalculated as waveform components, and said waveform components are stored in memory blocks identified by block addresses each composed of an M-level sequence with a length of (k/N) digits corresponding to said sequence of (k/N) elementary waveforms, in the order of time series specified by an additional scanning address;   a block address selector wherein N sets of M-level signal sequences for specifiying the first to the N-th sequences each including (k/N) elementary waveforms, formed so that the sum of said elementary waveforms of each set is equal to said M-level signal sequence, are selected on a time-shared basis and provided as said block address to said read-only memory;   a scanning address selector wherein N scanning addresses shifted from each other by a 1/N period (one symbol period) are selected on a time-shared basis in synchronization with the time-shared selection of said block addresses and provided as said additional scanning addresses to said read-only memory;   a demultiplexer wherein N parallel outputs obtained by demultiplexing N waveforms components read out of said read-only memory on a time-shared basis; and   an adder wherein N parallel outputs are added together and output as said multi-level band-restricted waveform.